1. Field of the Invention
The present invention relates to a vibration motor having an armature core being shifted and arranged around a rotating shaft with non-centrosymmetry.
2. Description of the Related Art
A vibration motor is used in portable telephone terminal and a pager and others. For example, a vibration motor of this type, as shown in Japanese Patent Laid-Open No. 9-182366, is a flat type vibration motor that is disclosed that an armature core on which winding (coils) wound is shifted and arranged around a rotating shaft with non-centrosymmetry so that vibration force generates.
FIG. 6 shows a vibration motor of this type. Armature core 20 has three salient poles 21, 22, 23. Salient pole 22 is located in the center thereof and salient poles 21, 23 are spaced apart by about 85xc2x0 from center salient pole 22 on either side. Coils 21a, 22a, 23a are wound on these salient poles, respectively. Rotating shaft 24 is (passed through and) fastened to a center of armature core 20. Furthermore, a flat type commutator that is not shown is arranged on one surface of armature core 20 around rotating shaft 24. In addition, cylindrical field magnet 25 faces an outer circumferential surface of armature core 20. Field magnet 25 is magnetized and divided into 6 poles.
A pair of brushes which is not shown are slidably in contact with the flat type commutator and coil 21a, 22a, 23a are energized, respectively. Thus, each of salient poles 21, 22, 23 of armature core 20 is excited. Armature core 20 rotates by means of magnetic action with field magnet 25. At this time, three salient poles 21, 22, 23 of armature core 20 are shifted and arranged. Therefore, a mass of armature core 20 is composed around rotating shaft in unbalance, the vibration motor occurs a strong vibration with a rotation of armature core 20.
As in the case of a commonly well-known motor, a vibration motor composed as above rotates (drives) by electromagnetic theory except that three salient poles 21, 22, 23 of armature core 20 are shifted and arranged. It is necessary to increase the mass of armature core 20 and the unbalance (distance of the center of gravity from the rotating shaft) in order to get a strong vibration. However, a cogging force that the mass unbalance contributed to is concentrated on because there is a little number of salient poles and those salient poles are shifted. As a result, there is the problem that the vibration motor does not start.
For the above problem, some solution can be obtained by which a lot of current is supplied to the coil and a starting force comes to be strong. On the other hand, a power consumption becomes big and as a result the new problem occurs that the vibration motor cannot be adopted a portable telephone and like that particularly in a use of being demanded a saving electric power.
The present invention, in consideration of the above problems, can make a starting force strong with maintaining saving electric power and is to provide a vibration motor which can increase a vibration force.
In order to achieve the above object, a vibrating motor according to claim 1 of the present invention is to provide a field magnet having 6 magnetic poles such that S and N magnetic poles are alternately magnetized (positioned) in a circumference direction, a rotating shaft, a armature core having three salient poles consisting of a central salient pole which are spaced apart from the central salient pole on either side, the three salient poles being shifted and arranged around the rotating shaft with non-centrosymmetry a coil being wound on each of said three salient poles; wherein; facing gap between the central salient pole and the field magnet is formed narrower than a facing gap between the auxiliary salient poles and the field magnet, an exciting force of the central salient pole is greater than that of the auxiliary salient poles; and, in starting, the same magnetic pole as the magnetic pole of the field magnet generates in a facing surface of the central salient pole and a repulsive force occurs so that the armature core is urged to rotate.
According to invention defined in claim 1, the facing gap between the central salient pole and the field magnet is formed narrower than the facing gaps between the auxiliary salient poles and the field magnet, the exciting force of the central salient pole is greater than that of the auxiliary salient poles, the repulsive force generating between the field magnet and the central salient pole is getting big (large), and, in starting, the same (magnetic pole) as the magnetic pole facing to the field magnet is generated in the central salient pole and the repulsive force occurs so that the armature core is urged to rotate. In addition, the pair of auxiliary salient poles is urged to rotate assistantly the armature core in a rotation direction by means of electromagnetic action between the auxiliary salient poles and facing field magnets and a direction of rotation in starting is getting constant.
Furthermore, the facing gap between the central salient pole and the field magnet is formed narrower than the facing gaps between the auxiliary salient poles and the field magnet. Thus, a center of gravity of the armature core which is shifted and arranged around the rotating shaft with non-centrosymmetry shifts to the central salient pole (side) so that it""s unbalance and a vibration becomes further stronger. In addition, the exciting force of the central salient pole is greater than that of the auxiliary salient poles and the armature core is urged to rotate as to center a repulsive force generating between the field magnet and the central salient pole. Thus, a cogging force of the vibration motor becomes big and the vibration is more strongly generated by the magnetic action.
In addition, a vibrating motor according to claim 2 of the present invention is characterized in that the facing surface of the central salient pole which is facing to the field magnet is formed approximately arc-shaped and each facing gap length on either side of a circumferential direction of the central salient pole is different.
According to invention defined in claim 2, the facing surface of the central salient pole, which is facing to the field magnet, is formed approximately arc-shaped and each facing gap length on either side of a circumferential direction of the central salient pole is different. Thus, in the condition that the armature core stops, the field magnet and the central salient pole are stable with approximately geometric center position. The center position is different from a magnetically center. When the same magnetic pole of the field magnet is generated and excited in the facing surface of the central salient pole from this condition, a big repulsive force occurs due to a difference of the magnetically center so that a starting force becomes big.
In addition, a vibration motor according to claim 3 of the present invention is characterized in that width of rib of the central salient pole on which the coil is wounded is formed greater than that (width of rib) of the auxiliary salient poles.
According to invention defined in claim 3, the width of rib of the central salient pole is formed great, so that an effective length of the coil becomes long and an excitation power of the central salient pole is getting big. Because a center of gravity of the armature core shifts in the central salient pole side, a vibration becomes further stronger.
A vibrating motor according to claim 4 of the present invention is characterized in that a number of turns of the coil wound on the central salient pole is bigger than that (number of turns) of the coil wound on (each of) the auxiliary salient poles and exciting force becomes large.
According to invention defined in claim 4, an excitation force of the central salient pole becomes large and a big repulsive force occurs so that a starting force increases and in addition, an urging force in order that the armature core rotates increases and a big vibration is provided.
A vibration motor according to claim 5 of the present invention is characterized in that a locus circle is made by facing surfaces between the field magnet and the three salient poles which is consisted of the central salient pole and the pair of auxiliary salient poles, and the locus circle is formed in in an approximately oval and a center of the field magnet and center of the locus circle approximately correspond with the rotating shaft.
According to invention defined in claim 5, the locus circle is made by the facing surfaces between the field magnet and the three salient poles which is consisted of the central salient pole and the pair of auxiliary salient poles and the locus circle is formed in the approximately oval and the center of gravity of the armature core shifts in the central salient pole side so that a vibration in a rotation becomes further stronger.
A vibration motor according to claim 6 of the present invention is characterized in that a locus circle is made by facing surfaces between the field magnet and the three salient poles which is consisted of the central salient pole and the pair of auxiliary salient poles, the locus circle is formed smaller than inside diameter of the field magnet, a center of the field magnet is almost coincident with rotating shaft and a center of the locus circle shifts (offsets) toward the central salient pole (side) from the rotating shaft.
According to invention defined in claim 6, the center of the locus circle which is made by facing surfaces between the field magnet and the three salient poles which is consisted of the central salient pole and the pair of auxiliary salient poles is offset toward the central salient pole (side) from the rotating shaft. Thus, the center of gravity of the armature core shifts in the central salient pole (side), the vibration in a rotation becomes further stronger.